Comprehensive Investigation of Transient Joule-Thomson Cooling and CO2 Hydrate Formation in Depleted Gas Reservoirs

Storing carbon in depleted gas reservoirs is crucial for mitigating global carbon dioxide (CO2) emissions. Injecting high-pressure CO2 into low-pressure reservoirs results in Joule-Thomson (JT) cooling caused by gas expansion. This temperature drop can lead to pore water freezing or the formation of CO2 hydrates, potentially affecting injectivity and compromising well integrity. These processes remain poorly understood due to their complexity and non-linear behavior. In this study, we present a coupled model that simulates non-isothermal fluid flow, hydrate formation kinetics, and the associated equations of rock properties. We verified this model using both steady-state and transient analytical solutions to analyze the dynamics of pore pressure propagation, thermal fronts, and fluid properties. Our results show that the developed model accurately captures the dynamics of these variables. Furthermore, we validated the model against experimental results, and it effectively predicts the spatial and temporal variations in pore pressure dynamics, both before and after the formation of CO2 hydrates. We applied the model to a field case (Viking gas reservoir), which has been considered for CO2 storage. We presented field test cases with injection temperatures (Tinj) of 75°C, 50°C, and 25°C . The analysis of the gas reservoir provided critical insights into pressure and temperature evolution, especially under the different injection temperatures for each test case. Notably, when Tinj =25°C, all test cases experienced the formation of CO2 hydrates in the highly permeable layers, significantly affecting pressure gradients both before and after encountering the permeability barrier. Therefore, the developed non-isothermal flow model, which incorporates hydrate formation kinetics, can be utilized in complex heterogeneous and simple homogeneous models to forecast the dynamics of physical processes during the injection of CO2 into depleted reservoirs.